The overall objective of this research is to understand the mechanism for and the regulation of the enzymatic synthesis of cholesterol and other water-insoluble substances by the liver. Specifically, we have identified and purified two specific soluble proteins, sterol carrier protein1 (SCP1) and sterol carrier protein2 (SCP2), which are required for liver microsomal cholesterol synthesis. SCP1 is required for the microsomal conversion of squalene to lanosterol, and SCP2 is required for the microsomal conversions of lanosterol to cholesterol. Studies will be conducted to further define the roles of these proteins in cholesterol metabolism.